Process and arrangement for evacuation of gas developed during a continuous metal refining operation

ABSTRACT

A PROCESS FOR DISCHARGING GAS DEVELOPED DURING A CONTINUOUS METAL REFINING OPERATION IN A REFINING APPARATUS INCLUDING A FIRST OR REACTION VESSEL AND A LAST VESSEL COMMUNICATING WITH THE FIRST VESSEL AND PROVIDED WITH A SLAG DISCHARGE OPENING COMMUNICATING WITH THE OUTER ATMOSPHERE, IN WHICH THE GAS IS EXHAUSTED THROUGH A PAIR OF CONDUITS RESPECTIVELY COMMUNICATING WITH SAID FIRST AND SAID LAST VESSEL AND IN WHICH THE AMOUNT OF GAS PASSING THROUGH THE PAIR OF CONDUITS IS REGULATED IN SUCH A MANNER THAT ESCAPE OF GAS THROUGH THE SLAG DISCHARGE OPENING IS POSITIVELY PREVENTED, AND AN ARRANGEMENT FOR CARRYING OUT THE PROCESS.

March 16, 1971 r J. ROUANET 3,570,831

PROCESS AND ARRANGEMENT FOR EVACUATION OF GAS DEVELOPED DURING A CONTINUOUS METAL REFINING OPERATION E Filed-Sept. 6, 1968 3 Sheets-Sheet 1 D/l awro Z JEAN Mum/E7 March 16, 1971 J. ROUANET 3,570,831

' PROCESS AND ARRANGEMENT FOR EVACUATION OF GAS DEVELOPED DURING A CONTINUOUS METAL REFINING OPERATION Filed Sept. 6. 1968 Y 3 Sheets-Sheet 2 Iwemwfl Ten/v Rea/war mp-40M ff r March 16, 1971 RQUANET 3,570,831

PROCESS AND ARRANGEMENT FOR EVACUATION OF GAS DEVELOPED DURING A CONTINUOUS METAL REFINING OPERATION Filed Sept. 6, 1968 U 3 Sheets-Sheet 3 United States Patent O 3,570,831 PROCESS AND ARRANGEMENT FOR EVACUA- TION OF GAS DEVELOPED DURING A CON- TINUOUS METAL REFHNING OPERATION Jean Rouanet, Metz, France, assignor to Institut de Recherches de la Siderurgie Francaise, St. Germain-en- Laye, Yvelines, France Filed Sept. 6, 1968, Ser. No. 757,954 Claims priority, application France, Apr. 18, 1967, 121,349; May 3, 1%8, 150,385 Int. Cl. (121cc 5/38 US. "Cl. 266-34 7 Claims ABSTRACT OF THE DISCLOSURE A process for discharging gas developed during a continuous metal refining operation in a refining apparatus including a first or reaction vessel and a last vessel communicating with the first vessel and provided with a slag discharge opening communicating with the outer atmosphere, in which the gas is exhausted through a pair of conduits respectively communicating with said first and said last vessel and in which the amount of gas passing through the pair of conduits is regulated in such a manner that escape of gas through the slag discharge opening is positively prevented, and an arrangement for carrying out the process.

BACKGROUND OF THE INVENTION The present invention relates to a process and an arrangement for evacuation of gas, more particularly of gas produced in a refining apparatus during a continuous refining of liquid metal therein.

The evacuation of gas developed during operation of a continuous metal refining apparatus causes sometimes problems which, due to the structure of the refining apparatus, are difficult to solve with gas discharge means known in the art. In apparatus for continuously refining metal, it is necessary not only to continuously discharge the gas developed during the refining operation, but also to continuously discharge the refined metal and the slag developed during refining process. The vessels of the refining apparatus require therefore at least one opening for the discharge of gas therefrom which develops during the refining operation and a plurality of additional openings, at least one of which, especially the opening which provides for the discharge of slag is in permanent communication with the outer atmosphere. It will therefore be evident that certain problems are created if it is desired to prevent any escape of gas developing during the refining process through the opening provided for the discharge of slag from the apparatus. Prevention of discharge of gas developing during the refining process through the slag discharge opening is, however, important since, as known, proper control of the refining process requires a constant measuring and analysis of the gas produced during the refining process. For instance, during refining of pig iron into steel, the amount of gas developed during the refining process is continuously measured and the amount of carbon monoxide and carbon dioxide contained in the gas is continuously determined in order to determine the decarburization of the liquid metal. It will therefore be evident that it is necessary to provide evacuation means which permit to collect or capture the entire gas developing during the refining process and to avoid raising of the pressure in the interior of the vessels of the refining apparatus in such a manner that would lead to a loss of gas so that in consequence thereof part of the carbon contained in the gas in the form of CO or CO would not be encompassed by the analysis of the gas.

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Another difficulty results from the fact that installations for continuously refining of metal usually comprise a plurality of vessels in communication with each other in which the various operations necessary for producing a refined metal are carried out and that it is difficult to determine the most favorable location of the opening for discharging the gas. Thus, if a single exhaust conduit is considered, it is difiicult to determine the location of this conduit and the rate of How therethrough in order to avoid any discharge of gas and also suction of air from the outer atmosphere into the apparatus. While suction of air from the outer atmosphere into the apparatus would not detrimentally eiiect the determination of the carbon content of the gas developed during the refining process or control of the refining operation in dependence of the carbon content measured, such sucking of air from the outer atmosphere into the interior of the refining apparatus has, if relatively large, the additional disadvantage to raisethe temperature of the said gas considerably by combustion of CO and to increase also the risk of causing considerable solution or" nitrogen in the metal. Therefore, it is also necessary to limit as far as possible suction of air from the outer atmosphere into the refining apparatus, and if possible, to reduce such suction of air into the apparatus to substantially zero.

It is an object of the present invention to overcome the above-discussed difiiculties and to provide for a process and an arrangement for the evacuation of gas developed during a continuous metal refining operation which will assure that the total amount of gas developed during the refining operation is captured without any loss of gas to the atmosphere, especially without any loss through the slag discharge opening of the apparatus.

'It is also an object of the present invention to provide for a process and an arrangement of the aforementioned kind in which also sucking of the air from the outer atmosphere through the slag discharge opening into the interior of the apparatus is reduced to a minimum and preferably held to substantially zero.

SUMMARY OF THE INVENTION The process according to the present invention of evacuating gas developed during a continuous metal refining operation is used in a metal refining apparatus including a first or reaction vessel and a last vessel communicating with the reaction vessel and having a slag discharge opening communicating with the outer atmosphere, in which the reaction vessel and the last vessel are provided with gas discharge conduits for discharging gas developing during the refining operation therefrom, and the process comprises the steps of exhausting gas through the conduit communicating with the reaction vessel at an amount q which is inferior to the total amount of gas Q developing during the refining operation, and simultaneously regulating the amount of gas exhausted through the conduit communicating with the last vessel to a value q substantially equal to the difference Q-q so as to obtain in the region of the slag discharge opening an equilibrium between the gas pressure in the interior of the apparatus and the pressure of the outer atmosphere to thus avoid any loss of gas through the slag discharge opening.

The process may also include the steps of continuously measuring the difference between the pressure p, of the gas pressure in the interior of the apparatus in the region of the slag discharge opening and the pressure p of the outer atmosphere in the region of the aforementioned slag discharge opening and to regulate the amount of gas exhausted through the aforementioned conduits in such a manner that the difference Ap=p p becomes substantially zero.

The amount of gas discharged through the aforementioned conduits may be automatically regulated by means of control means in dependence on the value of Ap.

The arrangement according to the present invention for carrying out the above-mentioned process may include a pair of gas discharge conduits respectively communicating at one of the ends therof with the reaction vessel and the last vessel, a common conduit communieating at one end with the other ends of the pair of gas discharge conduits, means provided in said common conduit and in at least one of the pair of gas discharge conduits for regulating the amount of gas passing therethrough, means for continuously measuring the difference Ap between the presure [1 of the outer atmosphere in the region of the slag discharge opening and the gas pressure 12 in the interior of the last vessel in this region, and control means cooperating with the measuring means and the regulating means in the conduits for automatically controlling the regulating means in dependence on the pressure difference Ap measured by the measuring means.

The arrangement according to the present invention for carrying out the process may also be characterized by the following features applied singly or in combination:

(a) The aforementioned common conduit may communicate at the other end thereof with a hood which is not fluid-tightly joined to the other end of the common conduit.

('b) The aforementioned common conduit may be connected by means of a conduit directly with an exhaust ventilator.

(c) The aforementioned common conduit may be arranged substantially vertically so that exhaustion of gas therethrough is caused by the chimney effect provided by the common conduit.

(d) The regulating means in the conduits may be constituted by vanes.

(e) The aforementioned regulating means may be constituted by ejector means for ejecting a neutral gas into the conduits.

Basically the invention permits, by adjusting the amount of gas exhausted through the conduits, to obtain an equilibrium between the gas pressure in the interior of the apparatus in the region of the slag discharge opening and the pressure of the outer atmosphere in the aforementioned region in order to collect the total amount of gas developed during the refining process. The aforementioned equilibrium will obviously be realized when the total amount of gas discharged through the conduits will be equal to the total amount of gas which is produced during the refining process. The equilibrium between the aforementioned pressures will assure that aspiration of air from the outer atmosphere through the slag discharge opening will be reduced to a minimum or become zero. In this way it is possible to conduct the gases developed during the refining process out of the apparatus without causing a combustion of the gases, which will produce the same advantages as are derivable from the conducting of gases without combustions in converters by means know in the art.

With the evacuation of the gas in the aforementioned manner it is possible to properly analyze the gas and to assure by this proper analysis a control of the refining process without error.

The invention also permits, by properly controlling the regulating means in the gas discharge conduits to limit the amount of gas discharged through the conduit connected to the first vessel of the apparatus and to such through the aforementioned conduit only a fraction q of the total amount Q of the gas developed during the refining process, while the remaining fraction q is stroked out through the conduit connected to the last vessel of the refining apparatus. In this way it is possible to create transversely through the vessels of the apparatus a circulation of the hot gas created in the first vessel of the refining apparatus, called the reaction vessel, and such circulation may be adjusted in any manner desired as a function of the refining process.

This feature is especially important since the circulation of the hot gases permits to maintain the interior of the vessels of the apparatus and the material contained therein at a temperature best suited for the refining process and to improve in this way the thermal balance of the apparatus. Especially, it is possible, due to the calories supplied by the hot gas stream to maintain the slag produced at a sufificiently elevated temperature so that the slag will remain fluid and easy to evacuate.

It is evident that the arrangement according to the present invention lends itself easily to an automatic control. For this purpose it is sufficient to provide in the regions of the openings in communication with the outer atmosphere measuring means for measuring the internal and external gas pressure in these regions and to control, by means of control means, the regulating means in the gas discharge conduits in such a manner to obtain an equilibrium between the internal and the external pressure at these regions.

The invention may be carried out in various different ways. Thus, one of the gas discharge conduits, for example the conduit connected to the reaction vessel may be deprived of means for regulating the amount of gas passing therethrough. Since the total amount Q of gas produced during a normal refining operation is known, it is possible to fix in advance the amount of gas q passing through the aforementioned conduit at a value considerably lower than Q, for instance three-quarters of Q. Since the amount of gas to be discharged through the aforementioned conduit is constant and determined in advance, it will sufiice to construct the aforementioned conduit with a diameter such that the pressure drop in this conduit will limit the amount of gas discharged therethrough substantially to the aforementioned amount q. The control means in this case have to control only the regulating means in the conduit connected to the last vessel of the apparatus and eventually also to the regulating means in the common conduit so as to adapt the total amount of gas discharged through the conduits to the total amount of gas produced and also to follow small variations of the total amount of the valve Q.

The arrangement of the common conduit which is connected to the gas discharge conduits respectively communicating with the first and the last vessel of the apparatus may likewise be made in different ways. The common conduit may for instance be rather short and discharge into a hood, as commonly used in converters while the hood is by means of another conduit connected to an exhaust ventilator. It is also possible to connect the common conduit directly by a conduit forming a continuation of the common conduit to an exhaust ventilator. On the other hand, it is possible to use for the common conduit a conduit which is relatively long and vertically arranged so that the chimney effect produced by the COIllmon conduit will provide an aspiration sufiicient for evacuation of the total amount of gas produced during the refining operation.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic sectional side view of the apparatus according to the present invention; and

FIGS. 24 respectively illustrate in part variations of the arrangement shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawing, and more specifically to FIG. 1 of the same, it will be seen that the apparatus for continuously refining pig iron into steel according to a process known mainly comprises a first vessel into the bottom of which the metal M to be refined is introduced through an inlet passage 10' and into which refining agents are injected under pressure by means of a lance 11 extending downwardly through the roof of the vessel 10. The slag metal foam formed in this way in the vessel 10 is evacuated from the latter by overflow into a second or last vessel 12 communicating with the first vessel 10 through the opening 12' in which the slag metal foam separates in a continuous metal phase and a slag phase floating thereon and the slag floating on the metal is continuously discharged through a slag discharge opening 13 which communicates with the outer atmosphere, while the metal is continuously discharged through an opening 13' in the bottom of the vessel 12. The apparatus and the process so far described are known in the art and for instance disclosed in the copending application Ser. No. 667,473.

The arrangement for evacuation of the gas produced during the refining process is constituted according to the present invention by a first conduit 14 communicating at one end thereof with an upper portion of the vessel 10 and by a second conduit 15 communicating at one end thereof with an upper portion of the vessel 12 in the region of the slag discharge opening 13 of the latter. The two gas discharge conduits 14 and 15 are connected at the other ends thereof to a common conduit 16 which extends in upward direction and which is provided in the interior thereof with means for regulating the flow of gas therethrough which, in the arrangement shown in FIG. 1, are constituted by a vane 17 turnable about an axis 17' so as to restrict more or less the open cross section of the common conduit 16. The conduit 16 discharges at its upper end into a hood 18 connected by a conduit 19 to an exhaust ventilator 20. This arrangement has the advantage to provide the function of a safety or overpressure valve, but this arrangement is not absolutely necessary.

Instead of the hood arrangement shown in FIG. 1, it is also possible to connect the upper end of the common conduit 16 by means of a conduit 21 forming a continuation of the conduit 16 directly to the exhaust ventilator as shown in FIG. 2. This latter arrangement is equivalent to the hood arrangement of FIG. 1 when the pressures outside and inside the hood are balanced, as it is commonly the case in the converters.

Considering the suction provided during normal operation of the ventilator 20, the amount of evacuated gas is regulated by the vane 17 to a valve equal to the amount Q developed during the refining operation in the apparatus.

The cross section ".s of the conduit 14 is determined in such a manner to be considerably smaller than a section which would normally permit the evacuation of the total amount of gas produced during the refining operation in the reaction vessel 10 through the conduit 14. In other words, the conduit 14 is arranged for the discharge of an amount of gas q considerably smaller than the total amount of gas Q normally developed during the refining operation. Therefore, a slight overpressure will be created in the vessel 10 and part of the gas developed therein will be passed into the decanting vessel 12. This part corresponds to an amount equal to Q-q.

The conduit 15 is provided with means for regulating the amount of gas passing therethrough, and these means are shown in FIG. 1 as a vane 2-2 turnable about an axis 22. The cross section S of the conduit 15 has a larger dimension than the cross section .s of the conduit 14. The cross section 8" is chosen in such manner so that, when the vane 22 is in fully open position, a strong sucthe gas made by an analyzer 23 connected for instance to the conduit 19, as shown in FIG. 1, will therefore be representative of the gas produced during the refining operation and it is possible to control in this way the refining operation With great precision. The aforementioned position of the vane 22 will correspond to an equilibrium between the pressure p, in the interior of the decanting vessel 12 in the region of the slag discharge opening 13 and the pressure p,, of the outer atmosphere in this region. The arrangement according to the present invention includes also means 24a and 24b arranged in the region of the slag discharge opening 13 for respectively measuring the pressure p, and the pressure p,, and to determine the ditference Ap=p p The vane 22 has therefore to be positioned in dependence on the value of Ap. In principle the vane 22 should be positioned in such a manner that the value Ap=0, but the vane may also be positioned that this value will become slightly negative, which corresponds to a small aspiration of air from the outer atmosphere through the slag discharge opening '13 into the vessel 12. The latter position has a certain advantage, especially if the refining operation is subjected to abnormal variations. Proper positioning of the vanes 17 and 22 is preferably made fully automatic. For this purpose the arrangement includes also control means including a regulator 25 of known construction, not forming part of the present invention, connected at the one hand to the pressure sensing means 24a and 24b and receiving from the latter a signal corresponding to Ap, and on the other hand to servo motors, or the like, 26 and 27 respectively connected, in a manner known per se and not forming part of the present invention, to the vanes 22 and 117 so as to position the latter in dependence on the pressure difference sensed by the pressure sensing means 24a and 24b. The position of the two vanes relative to each other will determine the amount of hot gas which, coming from the reaction vessel 10, will circulate through the decanting vessel 12.

The possibility of this additional regulation is especially interesting since it permits to influence the thermal balance of the arrangement. In this way it is possible to increase the ratio q/q, that is the portion of hot gas produced in the vessel 10 which will flow into the vessel 12 to be finally evacuated by the conduit 15, by changing the position of the vane 22 with regard to the vane 17 in the sense of a greater opening. This relative position of the two vanes can evidently be established by introducing a corresponding adjustable command input into the regulator 25.

The modification illustrated in FIG. 2 in which the common conduit 16 is directly connected by a conduit 21 to the exhaust ventilator 20 has certain advantages over the arrangement illustrated in FIG. 1. In fact, if it is desired to conduct the refining gases produced without combustion of the same in the manner as it is commonly carried out in converters, the use of a conduit which directly connects the common conduit 16 to the ventilator makes a supplementary regulation for equalizing the pressure in the interior and at the exterior of the hood 18 unnecessary.

In the modification shown in FIG. 3 no additional ventilator is used. In this case the elongated common conduit 16 is vertically arranged so that the hot gases passing therethrough will provide a chimney effect furnishing the necessary draft.

This arrangement has the advantage of great simplicity and it can be used for instance if it is not necessary to remove the dust from the gas or when it is not desired to recover the gas produced during the refining operation.

In all modifications described it is evidently possible to omit the vane 22 in the conduit and to reduce the diameter thereof and to place a vane in the conduit 14. Such an arrangement will function in the same manner as described above.

It is also possible to replace the vanes by other appropriate elements, for instance by ejectors. Such an arrangement is shown in FIG. 4 in which ejectors 28 and 29 are respectively arranged in the common conduit 16 and in the conduit '15. These ejectors are supplied with nitrogen under pressure from a source not shown in the drawing. The amount of nitrogen respectively blown through the ejectors 28 and 29 is respectively regulated by valves 30 and 31, the position of which may be controlled by servo motors 32 and 33 which in turn are operated from the regulator 25 in the manner as described above in connection with the vanes 117 and 2 2.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of method and arrangement for evacuating gas produced during a continuous refining operation differing from the types described above.

While the invention has been illustrated and described as embodied in a method and arrangement for evacuation of gas produced during a continuous metal refining operation in a metal refining apparatus, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. In combination with a refining apparatus for continuous metal refining and including a reaction vessel and a last vessel communicating with the reaction vessel and being provided at an end thereof distant from the reaction vessel with a slag discharge opening communicating with the atmosphere; an arrangement for evacuating gas developing during refining of metal in the apparatus without any loss of gas through said slag discharge opening, said arrangement comprising a pair of gas discharge conduits respectively communicating at one of the ends thereof with said reaction vessel and said last vessel; a common conduit communicating at one end with the other ends of said pair of gas discharge conduits; means provided in said common conduit and in at least one of said pair of gas discharge conduits for regulating the amount of gas passing therethrough; means for continuously measuring the difference A between the gas pressure p in the interior of said last vessel in the region of said slag discharge opening and the pressure 2 of the outer atmosphere in the region of the slag discharge opening; and control means cooperating with said measuring means and said regulating means in said conduits for automatically controlling said regulating means in dependence on the pressure difference Ap measured by said measuring means.

2. The arrangement as defined in claim 1, wherein said regulating means are constituted by vanes respectively mounted in said conduits movable between a plurality of positions by said control means in which said vanes restrict the cross section of said conduits to a varying degree.

3. The arrangement as defined in claim 1, wherein said regulating means are constituted by ejector means for ejecting a neutral gas respectively into said conduits, and wherein said control means cooperate with said ejector means for regulating the amount of neutral gas ejected into said conduits, respectively.

4. The arrangement as defined in claim 1, and including a hood arranged adjacent but spaced from the other end of said common conduit substantially coaxially therewith, and exhaust means connected to said hood for exhausting gas therefrom.

5. The arrangement as defined in claim 1, and including a conduit connecting the other end of said common conduit to an exhaust ventilator.

6. The arrangement as defined in claim 1, wherein, said common conduit extends in substantially vertical direction so that exhaustion of gas therethrough is caused by the chimney effect provided by said common conduit.

7. The arrangement as defined in claim 1, and including a gas analyzer connected to said common conduit.

References Cited UNITED STATES PATENTS 3,218,158 11/1965 Dumont-Fillon 60 3,475,599 10/ 1969 Schwartzenberg et al.

235--15 1.35 3,486,882 12/1969 Raguin et al. 75-51 GERALD A. DOST, Primary Examiner US. Cl. X.R. 75-46, 59 

